Chaetochromones A and B, two new polyketides from the fungus Chaetomium indicum (CBS.860.68)

Efficacy of ergosterol peroxide obtained from the endophytic fungus Acrophialophora jodhpurensis against Rhizoctonia solani

AIM

To investigate antifungal activity of the extract and major metabolite of the endophytic fungus Acrophialophora jodhpurensis (belonging to Chaetomiaceae) against crown and root rot caused by Rhizoctonia solani (teleomorph: Thanatephorus cucumeris), as an important pathogen of tomato.

METHODS AND RESULTS

The endophytic fungus A. jodhpurensis, has high inhibitory effect against R. solani AG4-HG II in vitro and in vivo. The media conditions were optimized for production of the endophyte's metabolites. The highest amounts of secondary metabolites were produced at pH 7, 30°C temperature, and in the presence of 0.5% glucose, 0.033% sodium nitrate, and 1 gl-1 asparagine as the best carbon, nitrogen, and amino acid sources, respectively. The mycelia were extracted by methanol and the obtained extract was submitted to various chromatography techniques. Phytochemical analysis via thin-layer chromatography (TLC) and nuclear magnetic resonance (NMR) spectroscopy showed that ergosterol peroxide was the major component in the extract of this endophyte. Antifungal activities of the methanolic extract and ergosterol peroxide in the culture media were studied against R. solani. Minimum inhibitory concentrations of the extract and ergosterol peroxide against the pathogen were 600 and 150 µg ml-1, respectively. Ergosterol peroxide revealed destructive effects on the pathogen structures in microscopic analyses and induced sclerotia production. Histochemical analyses revealed that it induced apoptosis in the mycelia of R. solani via superoxide production and cell death. Application of ergosterol peroxide in the leaf disc assay reduced the disease severity in tomato leaves.

CONCLUSIONS

Antifungal metabolites produced by A. jodhpurensis, such as ergosterol peroxide, are capable of controlling destructive Rhizoctonia diseases on tomato.

Key insights into secondary metabolites from various Chaetomium species

Endophytic fungi have proved to be a major source of secondary metabolites, wherein the genus Chaetomium has emerged as a source of multifarious bioactive natural compounds belonging to diverse classes such as chaetoglobosins, epipolythiodioxopiperazines, azaphilones, xanthones, anthraquinone, chromones, depsidones, terpenoids, and steroids. The objective of this review is to encapsulate recent findings on various Chaetomium strains, such as C. globosum, C. cupreum, C. elatum, C. subspirale, C. olivaceum, C. indicum, and C. nigricolor known for production of beneficial secondary metabolites, with an insight into their origin and function. A thorough literature survey was conducted for obtaining Chaetomium-derived secondary metabolites, with a scope of future application into drug development efforts. More than 100 secondary metabolites, with various beneficial properties such as antitumor, cytotoxic, antimalarial, and enzyme inhibitory activities, were enlisted. We believe this review will enhance the understanding of beneficial effects conferred by various Chaetomium-derived secondary metabolites and emphasize their potential in serving novel drug development efforts. KEY POINTS: • Identified Chaetomium-derived metabolites with potential for drug development. • More than 100 beneficial metabolites are enlisted. • Benefits include anti-cancerous, antimalarial, and anti-enzymatic properties.

Cytochalasans and azaphilones: suitable chemotaxonomic markers for the Chaetomium species

The accurate taxonomic concept of the fungal Chaetomium species has been a hard work due to morphological similarity. Chemotaxonomy based on secondary metabolites is a powerful tool for taxonomical purposes, which could be used as an auxiliary reference to solve the problems encountered in the classification of Chaetomium. Among secondary metabolites produced by Chaetomium, cytochalasans and azaphilones exhibited a pattern of distribution and frequency of occurrence that establish them as chemotaxonomic markers for the Chaetomium species. This review attempted to elucidate the composition of the Chaetomium species and its relationship with classical taxonomy by summarizing the pattern of cytochalasans and azaphilones distribution and biosynthesis in the Chaetomium species. KEY POINTS: • Secondary metabolites from the genus Chaetomium are summarized. • Cytochalasans and azaphilones could be characteristic metabolites of the Chaetomium species. • Cytochalasans and azaphilones could be used to analyze for taxonomical purposes.

Solieritide A, a new polyketide from the red alga Solieria sp

A new polyketide, solieritide A (1), along with six known ones (2-7), had been isolated from the red alga Solieria sp. The structures of these compounds were elucidated by spectroscopic analysis. The absolute configuration of 1 was determined by the method of X-ray diffraction. Compound 1 was a rare polyketide bearing benzopyrone ring fused with γ-butyrolactone. Compounds 2-7 were isolated from the red algae of genus Solieria for the first time. The antibacterial activities of 1-7 were also discussed.

Cytotoxic and antimicrobial indole alkaloids from an endophytic fungusChaetomiumsp. SYP-F7950 ofPanax notoginseng

Two new compounds chetoseminudin F (1) and G (2) together with eleven known compounds were isolated from the solid fermentation products of the endophytic fungus Chaetomium sp. SYP-F7950. The structures of the isolated compounds were elucidated by extensive spectroscopic analyses, including 1D and 2D NMR, and HRFABMS experiments. The absolute configurations of chetoseminudin F (1) and G (2) were determined by comparing the electronic circular dichroism (ECD) spectrum with those of the reported references. A plausible biogenetic pathway for compounds 1–6 and 9–13 was proposed. These isolates were also evaluated for their antimicrobial and antitumor activity, revealing that chetoseminudin F (1) displayed more potent cytotoxicity against MDA-MB-231 cells with an IC₅₀ value of 26.49 μmol L⁻¹ more than the common chemotherapeutic agent (paclitaxel). In antimicrobial assay, compounds 6, 9, 11 and 12 had strong antibacterial activity against Staphylococcus aureus, Bacillus subtilis, Enterococcus faecium and antifungal activity against Candida albicans with minimum inhibitory concentration (MIC) values ranging from 0.12 to 9.6 μg mL⁻¹; meanwhile compounds 6, 8, 9 and 12 exhibited strong cytotoxicity with IC₅₀ values of 2.75–8.68 μmol L⁻¹ against tumor cell lines A549 and MDA-MB-231. In addition, morphological observation showed that treatment with compounds 6, 9 and 12 increased the mean length of B. subtilis by 1.6 to 1.8-fold. In silico molecular docking was applied to study the binding interactions between the compounds and the active sites of filamentous temperature-sensitive protein Z (FtsZ) from B. subtilis. Compounds 6, 9 and 12 displayed the low binding energies, strong H-bond interactions with FtsZ. On the basis of the antimicrobial activities, cellular phenotype observation and docking studies, compounds 6, 9 and 12 are considered to be a promising antimicrobial inhibitor of FtsZ.

Two new compounds chetoseminudin F (1) and G (2) together with eleven known compounds were isolated from the solid fermentation products of the endophytic fungus Chaetomium sp. SYP-F7950.

Chromone Derivatives and Other Constituents from Cultures of the Marine Sponge-Associated Fungus Penicillium erubescens KUFA0220 and Their Antibacterial Activity

A previously unreported chromene derivative, 1-hydroxy-12-methoxycitromycin (1c), and four previously undescribed chromone derivatives, including pyanochromone (3b), spirofuranochromone (4), 7-hydroxy-6-methoxy-4-oxo-3-[(1E)-3-oxobut-1-en-1-yl]-4H-chromene-5-carboxylic acid (5), a pyranochromone dimer (6) were isolated, together with thirteen known compounds: β-sitostenone, ergosterol 5,8-endoperoxide, citromycin (1a), 12-methoxycitromycin (1b), myxotrichin D (1d), 12-methoxycitromycetin (1e), anhydrofulvic acid (2a), myxotrichin C (2b), penialidin D (2c), penialidin F (3a), SPF-3059-30 (7), GKK1032B (8) and secalonic acid A (9), from cultures of the marine sponge- associated fungus Penicillium erubescens KUFA0220. Compounds 1a–e, 2a, 3a, 4, 7–9, were tested for their antibacterial activity against Gram-positive and Gram-negative reference and multidrug-resistant strains isolated from the environment. Only 8 exhibited an in vitro growth inhibition of all Gram-positive bacteria whereas 9 showed growth inhibition of methicillin-resistant Staphyllococus aureus (MRSA). None of the compounds were active against Gram-negative bacteria tested.

Gα-cAMP/PKA pathway positively regulates pigmentation, chaetoglobosin A biosynthesis and sexual development in Chaetomium globosum

Sensing the environmental signals, the canonical Gα-cAMP/PKA pathway modulates mycelial growth and development, and negatively regulates some secondary metabolism in filamentous fungi, e.g. aflatoxin in Aspergillus nidulans. Here we report the characterization of this signaling pathway in Chaetomium globosum, a widely spread fungus known for synthesizing abundant secondary metabolites, e.g. chaetoglobosin A (ChA). RNAi-mediated knockdown of a putative Gα-encoding gene gna-1, led to plural changes in phenotype, e.g. albino mycelium, significant restriction on perithecium development and decreased production of ChA. RNA-seq profiling and qRT-PCR verified significantly fall in expression of corresponding genes, e.g. pks-1 and CgcheA. These defects could be restored by simultaneous knock-down of the pkaR gene encoding a regulatory subunit of cAMP-dependent protein kinase A (PKA), suggesting that pkaR had a negative effect on the above mentioned traits. Confirmatively, the intracellular level of cAMP in wild-type strain was about 3.4-fold to that in gna-1 silenced mutant pG14, and addition of a cAMP analog, 8-Br-cAMP, restored the same defects, e.g., the expression of CgcheA. Furthermore, the intracellular cAMP in gna-1 and pkaR double silenced mutant was approaching the normal level. The following activity inhibition experiment proved that the expression of CgcheA was indeed regulated by PKA. Down-regulation of LaeA/VeA/SptJ expression in gna-1 mutant was also observed, implying that Gα signaling may crosstalk to other regulatory pathways. Taken together, this study proposes that the heterotrimeric Gα protein-cAMP/PKA signaling pathway positively mediates the sexual development, melanin biosynthesis, and secondary metabolism in C. globosum.

Diversity and taxonomy of Chaetomium and chaetomium-like fungi from indoor environments

During a study of indoor fungi, 145 isolates belonging to Chaetomiaceae were cultured from air, swab and dust samples from 19 countries. Based on the phylogenetic analyses of DNA-directed RNA polymerase II second largest subunit (rpb2), β-tubulin (tub2), ITS and 28S large subunit (LSU) nrDNA sequences, together with morphological comparisons with related genera and species, 30 indoor taxa are recognised, of which 22 represent known species, seven are described as new, and one remains to be identified to species level. In our collection, 69 % of the indoor isolates with six species cluster with members of the Chaetomium globosum species complex, representing Chaetomium sensu stricto. The other indoor species fall into nine lineages that are separated from each other with several known chaetomiaceous genera occurring among them. No generic names are available for five of those lineages, and the following new genera are introduced here: Amesia with three indoor species, Arcopilus with one indoor species, Collariella with four indoor species, Dichotomopilus with seven indoor species and Ovatospora with two indoor species. The generic concept of Botryotrichum is expanded to include Emilmuelleria and the chaetomium-like species B. muromum (= Ch. murorum) in which two indoor species are included. The generic concept of Subramaniula is expanded to include several chaetomium-like taxa as well as one indoor species. Humicola is recognised as a distinct genus including two indoor taxa. According to this study, Ch. globosum is the most abundant Chaetomiaceae indoor species (74/145), followed by Ch. cochliodes (17/145), Ch. elatum (6/145) and B. piluliferum (5/145). The morphological diversity of indoor Chaetomiaceae as well as the morphological characteristics of the new genera are described and illustrated. This taxonomic study redefines the generic concept of Chaetomium and provides new insight into the phylogenetic relationships among different genera within Chaetomiaceae.

Phomopsichin A-D; Four New Chromone Derivatives from Mangrove Endophytic Fungus Phomopsis sp. 33

Four new chromone derivatives, phomopsichins A-D (1-4), along with a known compound, phomoxanthone A (5), were isolated from the fermentation products of mangrove endophytic fungus Phomopsis sp. 33#. Their structures were elucidated based on comprehensive spectroscopic analysis coupled with single-crystal X-ray diffraction or theoretical calculations of electronic circular dichroism (ECD). They feature a tricyclic framework, in which a dihydropyran ring is fused with the chromone ring. Compounds 1-5 showed weak inhibitory activities on acetylcholinesterase as well as α-glucosidase, weak radical scavenging effects on 1,1-diphenyl-2-picrylhydrazyl (DPPH) as well as OH, and weak antimicrobial activities. Compounds 1-4 showed no cytotoxic activity against MDA-MB-435 breast cancer cells. Their other bioactivities are worthy of further study, considering their unique molecular structures.